1. Field of the Invention
The present invention relates to induction machines and, more particularly, to end ring and bar joints associated with such motors and generators and related methods.
2. Description of Related Art
Over the years various induction machines, such as motors and generators, have been developed. Some of these machines conventionally include a stator that produces a rotating magnetic field and a rotor that rotates. Such stators and rotors are often coaxial cylinders. The rotor often includes a rotor shaft and a core having a plurality of laminated steel punchings or laminations substantially surrounding portions of the rotor shaft and in a substantially stacked arrangement. The rotor also has a plurality of conductor or rotor bars each spaced-apart and extending through (or otherwise associated with) the plurality of laminations. The rotor bars also often extend substantially parallel to an axis of the rotor shaft. The rotor additional can include a pair of end rings each positioned on an opposing end of the stacked plurality of laminations and connected to and supported by the rotor bars.
Examples of such induction motors and rotors can be seen in U.S. Pat. No. 6,566,778 by Hasegawa et al. titled “Cage-type Induction Motor For High Rotational Speeds,” U.S. Pat. No. 6,246,141 by Bailey titled “High Torque Reduced Starting Current Electric Motor,” U.S. Pat. No. 6,092,277 by Beltowski et al. titled “Rotor Bar Swaging Process,” U.S. Pat. No. 4,281,234 by Dohgne titled “Method Of Induction Annealing Squirrel Cage Rotors,” U.S. Pat. No. 4,249,098 by Karlen et al. titled “Squirrel-Cage Rotor Structure For An Asynchronous Electrical Motor,” U.S. Pat. No. 4,064,410 by Roach titled “Squirrel Cage Rotor And Method Of Making Same,” U.S. Pat. No. 2,200,126 by Smith titled “Damper Bar,” and U.S. Pat. No. 1,433,622 by Johnson et al. titled “Brazed Rotor Construction.”
Although many rotors of these induction machines have a somewhat simple and yet robust construction, as understood by those skilled in the art, for a high speed, high power density application, centrifugal and thermal stresses are non-trivial and require rigorous design of each of these major rotor components. For example, thermally induced stresses add further complexity to end ring design, and the high power density of certain machine implies that the operating temperatures of the rotor are relatively high, even with forced air-cooling. The temperature growth of the rotor, constructed of dissimilar metals with large differences in thermal expansion coefficients, results in high stresses at the end ring. In addition, differential growth can occur at high-speed and/or high-temperature conditions between the rotor core and end ring components due to differing density and coefficients of thermal expansion, resulting in a high shear load on the rotor bars and bar joints.
Accordingly, there is still a need for high strength induction machines, rotors, and end rings that enhance operation at high speeds and at high power density. There is also a need for enhanced induction machines, rotors, end rings, and rotor bar connections that can withstand high stress and high temperature conditions.